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ELECTRICITY AND MAGNETISM • Provide evidence that fields exist between objects exerting forces on each other even thogh the objects are not in contact Since ancient times, certain materials, called magnets, have been known to have the property of attracting tiny pieces of metal. This attractive property is called magnetism. S Bar Magnet S N N 1. Attract or repel other magnets 2. When allowed to swing freely one end will point magnetic north 3. Attract iron Inside a magnet ► -The smallest particle of an element is an atom ► -Atoms contain positively (protons) and negatively (electrons) charges particles ► Spinning electrons produce magnetic fields ► In magnets, the spinning electrons are aligned in domains that are in the same direction MAGNETISM Invisible force of “push” or “pull” by an object with this property Wagon does not move; forces are not lined up Hi! We’re e- (electrons)!!! We usually speed around the outside of the nucleus In these atoms, each e- is going its own way Wagon moves; forces are lined up But in a magnet or a metal, we can line up to become magnetic Lined up atoms/ electrons=Domain MAGNETS Domains 1. Have domain (lined up atoms) 2. Have polarity (characteristic of magnetism) North-seeking pole (“normal”) South-seeking pole (“reversed”) 3. Cannot have only 1 pole *** magnetic poles cannot be isolated*** 4. Like poles repel; Opposite poles attract Destroying Magnets ► When the magnetic domains are forced out of alignment, magnets will be destroyed. This can happen by heat or even a violent strike to a magnet with a hammer MAGNETS Materials whose atoms can be aligned Elements that can be magnetic 1. Fe: Iron soft iron loses magnetism easily 2. Co: Cobalt used to harden tools 3. Ni: Nickel used to make jewelry Other magnets: 1. Compass 2. Earth Iron filings N The strength of a magnet is concentrated at the ends, called north and south “poles” of the magnet. S W N S N Bar magnet S N E Compass Magnetic Forces: Like Poles Repel Unlike Poles Attract The area in which magnetic forces act We can describe magnetic field lines by imagining a tiny compass placed at nearby points. N S The direction of the magnetic field B at any point is the same Field B is strong where lines are dense and weak where as the direction lines are sparse. indicated by this compass. Where is the field strongest? MAGNETIC FIELDS An area where the force exists; area where force is felt Magnetic field lines 1. Leaves north pole & enters south pole 2. Lines closer together = stronger field NOTICE 1. Strongest at the poles 2. Field lines start at the NORTH pole and travel towards the SOUTH pole Earth is a Magnet ►A compass will point to magnetic north because a compass needle has a magnetized needle that spins freely. ► https://www.youtub e.com/watch?v=MZ tTVsIOA9c ELECTROMAGNET A magnet with a field produced by an electric current Electromagnetism a moving charge (electricity) produces a magnetic field ► More coils of wire= more current = stronger magnet ► Bigger battery/stronger current = stronger magnet Solenoids ► The magnetic field produced by a current has three distinct characteristics: the field can be turned on/off have its direction reversed have its strength changed. ► Solenoid: A coil of wire with a current. The two ends act like magnetic poles ► A solenoid with a ferromagnetic core is an electromagnet Increasing the Strength of electromagnets ► 1. increase the current in the solenoid ► Add more loops of wire to the solenoid ► Use a stronger ferromagnetic material Temporary Magnets ► Some materials like steel or iron can be easily magnetized, but lose their magnetism quickly. A magnet that easily loses its magnetism is called a temporary magnet https://mail.google.com/mail/u/0/#inbox/15add8d8ed16 5a5e?projector=1 CONDUCTORS A material, usually a metal, through which electrons can flow ► good conductor electrons able to move freely within the atoms of the material ► poor conductor or insulator electrons are not free to move about the atoms of the other material ELECTRIC CIRCUIT A path that allows electrons to flow from negative to positive ELECTRICITY MAGNETISM Electric currents cause magnetism ► How can you tell? Compass needle moves when near electrical current creating an magnetic field MAGNETISM ELECTRICITY Moving magnet can generate electricity ► How can you tell? Electromagnetic induction moving a magnet in and out of a coiled wire created an electrical current without a battery